This invention relates to water-in-oil emulsions of water-soluble cationic polymers and to processes for preparing such emulsions.
Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other monomers are well-known to be effective flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, metal or treatment, plating waste, coal tailings and the like. Particularly well known for these applications are the cationic carboxamide polymers such as copolymers of acrylamide and various cationic comonomers such as methacryloxyethyltrimethyl ammonium chloride.
In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymer in a water-in-oil emulsion wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, as well as a method for preparing them, are described in U.S. Pat. No. 3,284,393 to Vanderhoff et al. Unfortunately for many applications, these emulsions are not as stable and do not invert as readily as desired. In order to accelerate the inversion rate of such emulsions, it has been a common practice, e.g., as shown in U.S. Pat. No. RE 28,474, to add a water-soluble surfactant just prior to inversion. While the addition of an inverting surfactant in this manner does increase the rate of inversion, the resulting emulsions often do not exhibit the desired stability or the activity.
In view of the foregoing deficiencies of conventional emulsions and methods for inverting them, it is highly desirable to provide a stable water-in-oil emulsion that will invert quickly into an aqueous medium.